Abstract: System for secure authentication of a user's identity in an electronic system for banking transactions, said system comprising at least one first user apparatus subject to said secure authentication, and one or more further apparatuses bidirectionally communicating with each other and with said first apparatus, characterized in that: said first apparatus (?) and a second apparatus (?), belonging to said one or more further apparatuses, comprise an equal system generating a random number (M1) composed of any number of digits, said random number (M1) being divided into a first part and, respectively, a second part (SGN, CSGN), which are complementary and subsets of said random number (M1); said first apparatus (?) comprises means for generating, through said generating system, said first part (SGN) and sending it to said second apparatus (?); said second apparatus (?) comprises means for generating, through said generating system, said second part (CSGN) via generation of one or more of said random number (M